Java语言ReadWriteLock特性实例测试

本文研究的主要是ReadWriteLock特性，具体如下。

ReadWriteLock几点特性

readLock 与 readLock 不互斥
readLock 与 writeLock 互斥
writeLock 与 readLock 互斥
writeLock 与 writeLock 互斥

举例来说:

线程1, 先拿到readLock, 线程2试图拿readLock, 可以拿到
线程1, 先拿到readLock, 线程2试图拿writeLock, 阻塞等待,直到线程1释放锁之后才可以拿到
线程1, 先拿到writeLock,线程2试图拿readLock, 阻塞等待,直到线程1释放锁之后才可以拿到
线程1, 先拿到writeLock,线程2试图拿writeLock, 阻塞等待,直到线程1释放锁之后才可以拿到

测试代码

									package com.alioo.lock;

									import java.text.SimpleDateFormat;

									import java.util.Date;

									import java.util.concurrent.locks.Lock;

									import java.util.concurrent.locks.ReadWriteLock;

									import java.util.concurrent.locks.ReentrantReadWriteLock;

									/**

									 *

									 */

									public class ReadWriteLockDemo {

									    static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");

									    public static void main(String[] args) {

									        Data data = new Data();

									        Worker t1 = new Worker(data, false);

									        //写

									        Worker t2 = new Worker(data, true);

									        //读

									        Worker t3 = new Worker(data, true);

									        //读

									        t1.start();

									        t2.start();

									        t3.start();

									    }

									    static class Worker extends Thread {

									        Data data;

									        Boolean read;

									        public Worker(Data data, Boolean read) {

									            this.data = data;

									            this.read = read;

									        }

									        public void run() {

									            if (read)

									                data.read(); else

									                data.write();

									        }

									    }

									    static class Data {

									        ReadWriteLock lock = new ReentrantReadWriteLock();

									        Lock read = lock.readLock();

									        Lock write = lock.writeLock();

									        public void write() {

									            try {

									                Thread.sleep(2000);

									                //

									            }

									            catch (Exception e) {

									            }

									            write.lock();

									            System.out.println(Thread.currentThread() + " write:begin "

									                 + sdf.format(new Date()));

									            try {

									                Thread.sleep(5000);

									                //

									            }

									            catch (Exception e) {

									            }

									            finally {

									                System.out.println(Thread.currentThread() + " write:end "

									                      + sdf.format(new Date()));

									                write.unlock();

									            }

									        }

									        public int read() {

									            read.lock();

									            System.out.println(Thread.currentThread()+ " read :begin "

									                 + sdf.format(new Date()));

									            try {

									                Thread.sleep(5000);

									                //

									            }

									            catch (Exception e) {

									            }

									            finally {

									                System.out.println(Thread.currentThread() + " read :end "

									                      + sdf.format(new Date()));

									                read.unlock();

									            }

									            return 1;

									        }

									    }

									}

测试结果:

Thread[Thread-2,5,main] read :begin 2018-01-22 13:54:16.794
Thread[Thread-1,5,main] read :begin 2018-01-22 13:54:16.794
Thread[Thread-2,5,main] read :end 2018-01-22 13:54:21.795
Thread[Thread-1,5,main] read :end 2018-01-22 13:54:21.795
Thread[Thread-0,5,main] write:begin 2018-01-22 13:54:21.795
Thread[Thread-0,5,main] write:end 2018-01-22 13:54:26.795

测试结果解读:

同时启动了3个线程,其中1号线程Thread[Thread-0,5,main],执行write时先休眠了2秒.那么 2,3号线程Thread[Thread-1,5,main],Thread[Thread-2,5,main]将会优先执行代码